Apparatus and method for providing dual output signals in a telemetry transmitter

ABSTRACT

Telemetry transmitting apparatus and a method are provided for reception and transmission of heart related electrical signals, such as electrocardiogram (EKG) and/or cardiac pacemaker signals, from a plurality of electrodes coupled to the body of a medical patient. A receiving facility of the apparatus receives a plurality of analog signals representing at least the EKG signals. An output signal representing the EKG signals is formed and transmitted, via a wireless coupling, to a telemetry receiver. An analog output port is provided on the telemetry transmitting apparatus. The analog output port is also coupled to the receiving facility. A plurality of output signals representing the EKG signals is provided to the analog output port of the telemetry transmitting apparatus. The analog output port may be coupled to buffers at the input terminals of the apparatus. Alternatively, the output port may receive processed signals from the amplifier in the telemetry transmitter that are gain adjusted to emulate the unprocessed voltage signals of the EKG electrodes and then combined with a digital pace pulse signal so that the output signals include pacemaker pulse information.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.08/040,697, filed Mar. 31, 1993 now abandoned.

FIELD OF THE INVENTION

The present invention relates to apparatus and methods for distributingdata from a medical patient by way of a telemetry transmitting device.

BACKGROUND OF THE INVENTION

Telemetry transmitters provide a convenient means for remotelymonitoring the medical condition of a patient, i.e., monitoring heartrelated electrical signals, such as electrocardiogram (EKG) and cardiacpacemaker signals. The telemetry transmitter is connected to the patientby electrodes and wires. The telemetry transmitter includes terminalsfor receiving the EKG and pacemaker signals from the wires, and awireless transmitter that comprises, for example, a radio frequency (RF)link. Additional circuitry may be provided in the transmitter device foramplifying, filtering and multiplexing the received EKG and pacemakersignals. The transmitter sends the EKG and pacemaker signals to atelemetry receiver, which is typically in a central station.

It is often desirable to monitor the EKG and pacemaker signals locally.For example, a doctor or nurse may wish to review the EKG and/or thepacemaker signals while making his or her rounds. In some Telemetrytransmitters, such as the model 1481T Telemetry transmitter manufacturedby the Siemens Corporation, a display is provided for locally monitoringthe EKG signals. Although this provides convenience, it increases thecost of the telemetry transmitter.

An alternative method that allows local monitoring is to place atelemetry receiver in the patient's room and connect the telemetryreceiver to a monitor, as is done at the central station. Whileconvenient, this is also quite expensive. U.S. Pat. No. 3,882,277 toDePedro et al. describes such a telemetry system. A telemetry receiveris placed in the patient's room, and the receiver is connected to amodem for transmission over a conventional telephone system.

If the hospital has an EKG monitor available (for example, a mobiletransport monitor), the EKG electrodes that are attached to the patientcould be disconnected from the telemetry transmitter and reconnected tothe transport monitor for in-room monitoring. This method is costeffective, but is inconvenient, because the patient's EKG signal is notreceived at the central station while the EKG electrodes are connectedto the transport monitor. This method also requires that the caregiverperform four steps including: (1) disconnecting the electrodes from thetelemetry transmitter; (2) connecting the electrodes to the transportmonitor; (3) disconnecting the electrodes from the transport monitor,when local monitoring is completed; and (4) reconnecting the electrodesto the telemetry transmitter. Performing these steps takes up thecaregiver's valuable time.

Another problem associated with the method described above could occurwhile monitoring the quality of the electrode contacts. The quality ofthe EKG and pacemaker waveforms is affected by the quality of theelectrode contact to the skin, so viewing the EKG and/or pacemakerwaveforms from the bedside monitor via the telemetry transmitter allowsevaluation of the electrode contact in the patient's room. Using themethod described in the previous paragraph, the electrode contact may bedisturbed while performing steps (3) and (4). The caregiver would notimmediately become aware of this problem because he or she would nolonger be viewing the waveform on the transport monitor. The discrepancywould not be detected until someone viewed the waveform back at thecentral station. At that point, it would be necessary to dispatchanother person back to the patient's room to fix the electrode contact.

A convenient, low cost apparatus for locally monitoring the output of anEKG telemetry transmitter is desired.

SUMMARY OF THE INVENTION

The present invention is embodied in telemetry transmitting apparatusand a method for reception and transmission of medical data representinga medical condition of a patient, i.e., heart related electricalsignals, such as electrocardiogram (EKG) and/or cardiac pacemakersignals. The signals are received from a plurality of electrodes coupledto the body of a medical patient.

A receiving facility of the apparatus receives a plurality of analogsignals representing at least the EKG signals. An output signalrepresenting the EKG signals is formed and transmitted, via a wirelesscoupling, to a telemetry receiver.

An analog output port is provided on the telemetry transmittingapparatus. The analog output port is also coupled to the receivingfacility. A plurality of output signals representing the EKG signals isprovided to the analog output port of the telemetry transmittingapparatus. The output signals provided to the analog output port of thetelemetry transmitting apparatus, as well as those transmitted via thewireless coupling, may also represent the cardiac pacemaker signals.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram of an exemplary system according to theinvention.

FIG. 2 is a block diagram of an exemplary embodiment of the telemetrytransmitter shown in FIG. 1.

FIG. 3 is a block diagram of a second embodiment of the telemetrytransmitter shown in FIG. 1.

FIG. 4 is a block diagram of the decoder/attenuator circuit shown inFIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a block diagram of an exemplary system including a telemetrytransmitting apparatus 100 according to the invention. The telemetrytransmitting apparatus 100 receives a plurality of analog signalsrepresenting the patient's condition, which may be, for example heartrelated electrical signals, such as electrocardiogram (EKG) waveformsignals and pacemaker pulse signals acquired by a plurality ofelectrodes 120a-e coupled to the body of a medical patient 10. Thetransmitter provides means for forming and transmitting an output signal50 representing the EKG and pacemaker waveforms, via a wireless couplingto a telemetry receiver 20. The telemetry receiver 20 may be of aconventional type, and may be coupled to a central station 40 formonitoring the patient's condition remotely.

In accordance with the invention, the telemetry transmitter 100 alsoincludes an analog output port 118, which provides a plurality of analogoutput signals representing the EKG waveforms and pacemaker pulses. Anelectrical cable 34 may be used to connect the analog output port 118 ofthe telemetry transmitting apparatus 100 to the input port 32 of amonitor 30 in the patient's room. To view the EKG signals without thepacemaker pulses, monitor 30 may be any patient monitor capable ofreceiving EKG electrodes. To view the EKG signals with the pacemakerpulses, monitor 30 must be able to sense pacemaker spikes. For example,monitor 30 may be a conventional transport monitor, such as the SIRECUST630 transport monitor, manufactured by Siemens corporation.

Using the analog output port 118, a medical caregiver can easily connecta monitor 30, to the telemetry transmitter 100 without the need todisconnect the electrodes 120a-e from transmitter 100. The process ofconnecting the transmitter 100 to the monitor 30 only involves thesingle step of connecting the cable 34 to the output port 118 and theinput port 32. Similarly, disconnecting monitor 30 is performed in asingle step. There is no interruption in transmitting signal 50 to thetelemetry receiver 20 for remote monitoring during any of the periodswhen monitor 30 is being connected, when the patient's EKG withpacemaker activity is viewed locally, or when the monitor 30 is beingdisconnected. The EKG signals may be monitored locally, on monitor 30,and remotely, on monitor 40, at the same time.

Another benefit of the invention is that the caregiver can verify thequality of the EKG waveform that is transmitted by the telemetrytransmitter 100, without disturbing any existing connections. There isno need to disturb the electrodes to perform this evaluation. Cable 34is connected to port 118 of the telemetry transmitter 100 to start localmonitoring; and the cable 34 is unplugged from the port 118 when localmonitoring is completed.

FIGS. 2-4 show two exemplary embodiments of a telemetry transmitter 100and 200 in accordance with the invention.

FIG. 2 is a block diagram of an exemplary embodiment of the telemetrytransmitting apparatus 100 shown in FIG. 1. Transmitter 100 providesreception and wireless transmission of electrocardiogram (EKG) andpacemaker signals. The EKG signals are received from a plurality ofelectrodes LA, LL, RA, C and RL (shown in FIG. 1) coupled to the body ofa medical patient by electrode wires 120a-e. The electrodes are coupledto the left arm (LA), left leg (LL), right arm (RA), chest (C) and rightleg (RL) of the patient 10.

The EKG and pacemaker signals are received by transmitter 100 at aplurality of input terminals 111a-e. A plurality of buffers 112a-e arecoupled to the input terminals 111a-e. Each buffer 112a-e receives arespective analog signal from a respective EKG electrode LA, LL, RA, Cand RL. The terminals 111a-e and buffers 112a-e provide a means forreceiving the plurality of analog signals representing the EKG signals.Each buffer 112a-e is an amplifier that has unity gain and unityfeedback gain, with high input impedance and low output impedance. Thebuffers 112a-e hold the EKG data so that it may be provided to an EKGamplifier 102 and the analog output port 118. Buffers 112a-e areconnected to output port 118 by a plurality of electrical couplings116a-e and to EKG amplifier 102 by electrical connections generallyindicated by arrow 117.

Other elements of the telemetry transmitter 100 may be the same typecomponents as used in conventional telemetry transmitters. For example,EKG amplifier 102 includes an amplifier/combiner circuit 122 forboosting the EKG voltage signals, and for combining the input voltagesignals received from buffers 112a-e into three EKG lead signals. In theexemplary embodiment, the gain of amplifier/combiner circuit 122 is 500.The amplifier/combiner circuit 122 forms the three leads from the fiveinput voltage signals. The three leads are designated I, II, and V,which are the standard designations used in the field. Lead I is formedby the differential voltage between the left arm electrode LA and theright arm electrode RA, according to equation 1.

    I=LA-RA                                                    (1)

Lead II is formed by the differential voltage between the left legelectrode LL and the right arm electrode RA.

    II=LL-RA                                                   (2)

Lead V is formed by equation (3).

    V=C-(LA+RA+LL)/3                                           (3)

where: C, LA, RA and LL designate the signals returned by the respectivechest, left arm, right arm and left leg electrodes.

Amplifier 102 also includes a filter 124 coupled to the output ofamplifier/combiner circuit 122 for removing artifacts such ashigh-frequency noise (out of the frequency band of the EKG signal) fromthe EKG signal. Amplifier/combiner circuit 122 also removes any cardiacpacemaker pulse signals picked-up by the patient electrodes.

Therefore, a pace pulse detector 125 is coupled to also receive theoutput from amplifier/combiner circuit 122 for monitoring the EKG leadsignals produced thereby for the presence of cardiac pacer pulses. Pacepulse detector 125 produces a digital pulse signal 126 if a cardiacpacer pulse is detected on one or more of the three lead signals. Thepace pulse signal 126 can merely be a pulse indicating that a pacersignal has been detected, or a more elaborate signal which simulates thedetected pacer pulse. The precise nature of the pace pulse signaldeveloped by detector 125 is left to the designers' choice. Pace pulsedetectors conventionally include a slew-rate detector to detect therising or falling edges of a pacer signal. The construction andoperation of pace pulse detectors are well known to those of ordinaryskill in this technology, as shown, for example, by the pace pulsedetector descriptions in U.S. Pat. Nos. 4,934,376, 5,231,990, 5,025,808or 4,658,831. Thus, further description of detector 125 is notnecessary.

As is also conventional in EKG monitoring apparatus, "lead-off"detection and switching circuitry may also be provided, as described,for example, in U.S. Pat. Nos. 5,231,990 or 5,025,808. In theillustrated FIG. 2 embodiment, a lead-off detector/switch 127 is coupledto each of electrical couplings 116a-e to monitor the outputs of buffers112a-e to determine the sufficiency of electrical contact made by theEKG electrodes to the body of the patient, and control the connection ofcouplings 116a-e to output port 118 via couplings 128a-e. Each electrodesignal lead is monitored to determine if an electrode has come looseand/or disconnected, and if a loose and/or disconnected electrode signallead is found, a switch circuit portion of lead-off detector/switch 127de-couples that electrode signal lead and in its place substitutes alead having a good connection to the patient. For example, if monitoringof the RL signal on coupling 116e indicated that the RL electrode wasloose and/or disconnected, the C signal from coupling 116d could besubstituted therefor.

Wireless transmitting circuitry 103, 104, 106 and 108 may includeconventional transmitting devices, coupled to the receiving circuitry111a-e, 112a-e and 102, which form and transmit an output signal 50,representing the EKG and detected pace pulse signals, via a wirelesscoupling. In the exemplary telemetry transmitter 100, under the controlof a central processing unit (CPU) 103 and via electrical signalconnections indicated generally by arrow 130, a multiplexer 104 combinesthe EKG lead I, II and V signals into a single analog signal 105 that isapplied to an analog to digital (A/D) converter and formatter 106. It iscontemplated that multiplexer 104 may combine signals I, II and V usingtime-division multiplexing techniques or frequency division multiplexingtechniques. A/D converter and formatter 106 is also responsive to theoutput signals of pace pulse detector 125 and lead-off detector/switch127. Under the control of CPU 103 and via electrical signal connectionsindicated generally by arrow 130, a digital signal 107 is developed byA/D converter and formatter 106 which comprises a serial presentation ofinput data, such as the EKG lead data in a first data block, pacer datain a second data block and battery voltage and button status in thirdand fourth data blocks, respectively. Next, digital signal 107 isfrequency modulated by an R/F modem 108 and then applied to an antenna110 for transmission. The R/F modem 108 may include, for example,frequency shift keying (FSK) or quadrature amplitude modulation (QAM)circuitry.

Note, using the apparatus of FIG. 2, the signals received at the analogoutput port 118 are the same signals as those input to EKG amplifier102.

FIG. 3 is a block diagram of a second exemplary embodiment of atelemetry transmitter 200 constructed in accordance with the invention,wherein the signals received at the analog output port 118 are not thesame as those input to EKG amplifier 102, but signals reconstructed fromthe combined lead signals. Elements that are common between the twoembodiments (102, 103, 104, 106, 107, 108, 110, 111a-e, 118, and 128a-e)have the same reference numerals as the corresponding elements in FIG.2, for ease of identification. For brevity, the description of thesecommon elements is not repeated. Additionally, a lead-offdetector/switch similar to switch 127 shown and described in FIG. 2 isnot shown in the FIG. 3 embodiment, but could be incorporated ifdesired.

As is apparent from the drawing, analog output port 118 does not receiveunconditioned signals directly from the input terminals 111a-e, as isthe case in the embodiment of FIG. 2. Instead, the EKG lead signals I,II and V from leads 226a-c and output 126 of pace pulse detector 125 areprovided to a combination decoder/attenuator device 220, which separatesthe three lead signals into five analog output signals, 128a-e. Thedecoder/attenuator 220 decodes each one of the amplified signals I, IIand V, and attenuates the resulting individual signals to form aplurality of individual attenuated signals 128a-e that are substantiallyequal in magnitude to the respective analog signal LA, LL, RA, C and RLfrom which the amplified signals I, II and V are formed. Additionally,decoder/attenuator 220 places the digital pace signal from output 126 ofdetector 125 into the five analog output signals 128a-e.

In the embodiment of FIG. 3, there may be very small differences betweenthe values of output signals 128a-e and the actual EKG voltages, becausethe artifacts/high frequency signal components which are filtered out byfilter 124 are not restored by decoder/attenuator 220. For example, theoriginal cardiac pacemaker pulse signal is replaced by the digital pacesignal 126 provided by detector 125.

FIG. 4 shows an exemplary embodiment of a circuit to perform thefunctions of decoder/attenuator 220. In the exemplary embodiment, thevoltage of the right arm electrode RA is held at a reference potential(e.g., ground). With RA set to zero, equations (1) through (3) may berewritten to separate out the left arm, left leg and chest components asfollows:

    LA=I                                                       (4)

    LL=II                                                      (5)

    C=V+(I+II)/3                                               (6)

Additionally, all of the signals are reduced in magnitude by a constantfactor that is equal to the gain of amplifier 102 (shown in FIG. 3). Inthe exemplary embodiment, EKG amplifier 102 has a gain of 500, so thedecoder/attenuator 220 reduces all of the voltage signals by a factor of0.002.

The exemplary decoder/attenuator 220 is a voltage divider circuit.Although any number of circuits may be designed to perform the functionsdescribed above, the voltage divider provides a particularly inexpensivesolution for achieving the desired gain adjustment and performing thearithmetic operations defined by equations (4) through (6).

The left arm LA voltage is produced at node N1, between resistors R1 andR2. This portion of the voltage divider circuit implements equation (4),and performs the gain adjustment. In the exemplary embodiment, thedesired gain is 0.002, so the ratio of R2/R1 is 0.002. Exemplaryresistances are R1=100,000 Ohms, and R2=200 Ohms.

The left leg LL voltage is produced at node N2, between resistors R3 andR4. This portion of the voltage divider circuit implements equation (5),and performs the gain adjustment. In the exemplary embodiment, thedesired gain is 0.002, so the ratio of R4/R3 is 0.002. Exemplaryresistances are R3=100,000 Ohms, and R4=200 Ohms.

The Chest voltage is produced at node N3, between resistor R8 and theresistors R5, R6 and R7. This portion of the voltage divider circuitimplements equation (6), and performs the gain adjustment. In theexemplary embodiment, the desired gain is 0.002, so the ratio of R8/R5is 0.002, and R6/R8=R7/R8=1500. Exemplary resistances are R5=100,000Ohms, R6=R7=300,000 Ohms and R8=200 Ohms.

Decoder/attenuator 220 includes resistors R9, R10 and R11 coupledbetween the output of pace pulse detector 125 and nodes N1, N2 and N3,respectively, for adding pace pulse signal 126 to the five analog outputsignals 128a-e. Exemplary resistance values for resistors R9, R10 andR11 are 200,000 Ohms each.

It is understood by one of ordinary skill in the art that the use of avoltage divider to perform these arithmetic functions is most accurateand effective when there is a high gain in amplifier 102, so that theresistors R1, R3, R5, R6 and R7 are all much larger than R2, R4 and R8.In the exemplary embodiment, there are more than two orders of magnitudebetween the larger resistors and the smaller resistors, which issufficient to accurately perform the attenuation function.

It is also understood by one of ordinary skill in the art that anydevice coupled to receive one of the five signals LA, LL, RA, C and RLdescribed has a high input impedance so that the device does not changethe resistance ratios.

It is further understood that many other circuits or devices couldperform these functions, although the cost is likely to be higher. Forexample, attenuators containing active devices could be used to performthe gain adjustment. Furthermore, the choice of which EKG electrodes areused as the reference potential may be varied. In the exemplaryembodiment, the right arm RA and right leg electrodes RL are consideredto be ground. It would also be possible to use the left arm and left legas ground.

Although the invention has been described in terms of its applicabilityto EKG telemetry transmitters, it is understood that the invention maybe practiced in telemetry transmitters that transmit other forms ofmedical patient data (e.g., EEG, blood pressure, saturated oxygen ortemperature).

It is understood by one skilled in the art that many variations of theembodiments described herein are contemplated. While the invention hasbeen described in terms of exemplary embodiments, it is contemplatedthat it may be practiced as outlined above with modifications within thespirit and scope of the appended claims.

What is claimed:
 1. A portable patient monitoring apparatus adapted forbeing carried by a medical patient and having as its primary functionthe reception and then wireless transmission to a remote monitoringdevice of medical data acquired from the patient, and having a secondaryfunction of also providing the medical data to an output port of thetelemetry transmitter for facilitating local monitoring of the medicaldata, comprising:receiving circuitry adapted for being coupled to saidpatient for receiving a plurality of analog signals representing asensed condition of the patient; wireless transmitting circuitry,including a signal processor and a wireless signal transmitter coupledto the receiving circuitry for forming an output signal representing thepatient's condition and transmitting said output signal via a wirelesstransmission to a remote monitoring device; an analog output portincluded as part of the wireless transmitting circuitry; and outputmeans coupled to the receiving circuitry for providing a plurality ofanalog output signals representing the patient's condition to the analogoutput port of the wireless transmitting circuitry simultaneously withthe transmission of said output signal to the remote monitoring device.2. Apparatus in accordance with claim 1, wherein said analog signalsinclude analog EKG signals, and wherein the receiving circuitry includesEKG amplifying means responsive to the analog EKG signals for developingamplified EKG signals.
 3. Apparatus in accordance with claim 2,wherein:said EKG amplifying means includes a filter means for filteringsaid analog signals to develop said EKG signals; and further including,a pacemaker pulse detector responsive to said analog signals beforebeing filtered by said filter means for developing a pace pulse signaland providing said pace pulse signal to said wireless transmittingcircuitry for being included in said output signal being transmitted. 4.Apparatus in accordance with claim 3, wherein:said output means includesa lead-off detector/switch which is individually responsive to each ofsaid analog signals for sensing an insufficient coupling of saidreceiving circuitry to said patient, and for providing a substituteanalog signal to said analog output port in place of an insufficientlycoupled analog signal.
 5. Apparatus in accordance with claim 4,wherein:said lead-off detector/switch develops a lead-off sense signalwhich indicates insufficient coupling of said receiving circuitry tosaid patient, and a signal conduction path is provided for coupling saidsense signal to said transmitting circuitry for being included in saidoutput signal being transmitted.
 6. Apparatus in accordance with claim1, wherein:the receiving circuitry includes a plurality of buffers, eachbuffet receiving one of the plurality of respective analog signalsacquired from the patient; and the output means includes means forcoupling the buffers to the analog output port.
 7. Apparatus inaccordance with claim 6, wherein the receiving circuitry includes anamplifier coupled to the buffers, the amplifier amplifying eachrespective one of the plurality of analog signals.
 8. Apparatus inaccordance with claim 1, wherein;said analog signals include analog EKGsignals; the receiving circuitry includes:an amplifier coupled to thereceiving circuitry, the amplifier amplifying each respective one of theplurality of analog signals to form a respective amplified signal, andmeans for combining the plurality of amplified signals to form aplurality of EKG lead signals; the wireless transmitting circuitryincludes:a multiplexer coupled to receive the EKG lead signals whichcombines the EKG lead signals to form a single signal, an analog todigital converter which digitizes the single signal provided by themultiplexer, and a radio frequency modem which converts the digitalsingle signal into a radio frequency signal for wireless transmission tosaid remote monitoring device; and the output means includes:a voltagedivider circuit coupled to receive the EKG lead signals, for decodingthe EKG lead signals into a plurality of individual signals thatrepresent the respective analog signals before their amplification bythe amplifier by said receiving circuitry, circuitry.
 9. A patientmonitoring system, comprising:telemetry transmitting apparatus, locatedin a first housing, adapted for being carried by a medical patient andhaving as a primary function the reception and then wirelesstransmission to a remote monitor of electrocardiogram (EKG) dataacquired from the patient and having a secondary function of alsoproviding the EKG data to an output port of the telemetry transmittingapparatus for facilitating transfer of the EKG data to an input port ofa local monitor; a remote monitor, located in a second housing, havingan input port at which the wireless transmission of the EKG data fromthe medical patient are received for display; wherein said telemetrytransmitting apparatus comprises: receiving circuitry adapted for beingcoupled to said patient for receiving a plurality of analog signalsrepresenting the EKG data; transmitting circuitry, including a signalprocessor and a wireless signal transmitter coupled to the receivingcircuitry for forming an output signal representing EKG data of thepatient and transmitting said output signal via a wireless transmissionto said remote monitor; an analog output port included as part of thetransmitting circuitry; and output means coupled to the receivingcircuitry for providing a plurality of analog output signalsrepresenting the patient's EKG data to the analog output port of thetransmitting circuitry simultaneously with the wireless transmission ofsaid output signal to the remote monitor; and further including anelectrical cable connecting the analog output port of the transmittingcircuit to the input port of the local monitor.
 10. A patient monitoringsystem in accordance with claim 9, wherein said remote monitor comprisesa central monitoring station including:wireless communication means forreceiving the output signal; and a central station monitor coupled tothe wireless communications means for displaying EKG waveforms derivedfrom the received output signal.
 11. A patient monitoring system inaccordance with claim 9, wherein:said receiving circuitry includes afilter means for filtering said analog signals to develop said analogsignals representing EKG data; and further including, a pacemaker pulsedetector responsive to said analog signals before being filtered by saidfilter means for developing a pace pulse signal and providing said pacepulse signal to said transmitting circuitry for being included in saidoutput signal being transmitted.
 12. A patient monitoring system inaccordance with claim 9, wherein:said output means includes a lead-offdetector/switch, which is individually responsive to each of said analogsignals for sensing an insufficient coupling of said receiving circuitryto said patient, and for providing a substitute analog signal to saidanalog output port in place of an insufficiently coupled analog signal.13. A patient monitoring system in accordance with claim 12,wherein:said lead-off detector/switch develops a lead-off sense signalwhich indicates insufficient coupling of said receiving circuitry tosaid patient, and a signal conduction path is provided for coupling saidsense signal to said transmitting circuitry for being included in saidoutput signal being transmitted.
 14. A patient monitoring system inaccordance with claim 9, further including:a pacemaker pulse detectorresponsive to said analog signals for developing a pace pulse signal andproviding said pace pulse signal to said output means, and said outputmeans including combining means for adding said pace pulse signal tosaid analog output signals representing EKG data which are provided bysaid output means to said analog output port.
 15. A method for operatinga telemetry transmitter adapted for being carried by a medical patientand having as a primary function the reception of medical data acquiredfrom a plurality of sensor devices coupled to a medical patient, and forproviding via wireless transmission multiple signals to a remotelylocated display device for displaying the medical data, and having asecondary function of also providing the medical data to an output portof the telemetry transmitter for facilitating transfer of the medicaldata to a local display device, the method comprising the steps of:(a)receiving from the sensor devices a plurality of analog signalsrepresenting a condition of the patient, the receiving being performedby the telemetry transmitter; (b) forming an output signal representingthe medical data and transmitting said output signal to said remotelylocated display device via a wireless transmission; and (c) forming andtransmitting a plurality of analog output signals representative of theanalog signals recited in step (a) to the output port of the telemetrytransmitter for use by the local display device located proximate to thetelemetry transmitter simultaneously with the transmission of saidoutput signal to the remotely located display device.
 16. A method inaccordance with claim 15, wherein the sensor devices are EKG electrodes,and:step (a) includes the step of receiving a plurality of analogsignals representing EKG signals; step (b) includes the step of formingand transmitting an output signal representing the EKG signals; and step(c) includes the step of forming and transmitting a plurality of analogoutput signals representing the EKG signals.
 17. A method in accordancewith claim 16, further comprising the step of:(d) connecting the outputport of the telemetry transmitting apparatus to the local displaydevice, for locally displaying the EKG signals.
 18. A method inaccordance with claim 16, wherein step (b) includes the steps of:(1)amplifying the plurality of analog signals to form a plurality ofamplified signals, (2) combining the plurality of the amplified signalsto form a plurality of EKG lead signals, (3) multiplexing the pluralityof EKG lead signals to form a single signal, and (4) modulating a radiofrequency carrier with the single signal; and the method furthercomprises the step of: (f) transmitting the modulated signal from thetelemetry transmitter to said remotely located display device via thewireless transmission.
 19. A method in accordance with claim 18,including, between steps (1) and (2), the step of:(1a) filtering theplurality of amplified signals to attenuate signal components havingfrequencies outside of a band of frequencies occupied by the EKGsignals.
 20. A method in accordance with claim 16, wherein step (c)includes the further steps of:(3) sensing an insufficient coupling ofone or more of said electrodes to said patient, and in response to saidsensing providing a substitute analog signal to said output port inplace of an analog signal received from an insufficiently coupledelectrode.